Photographic material for the silver dyestuff bleaching process



United States Patent 3,394,004 PHOTOGRAPHIC MATERIAL FOR THE SILVER DYESTUFF BLEACHING PROCESS Walter Anderau, Aesch, Basel-Land, and Rene von Wartburg and Bernhard Pillar, Basel, Switzerland, assignors to Ciba Limited, Basel, Switzerland, a company of Switzerland No Drawing. Filed Mar. 16, 1965, Ser. No. 440,303 Claims priority, application Switzerland, Mar. 20, 1964, 3, 18/64 11 Claims. (Cl. 96-53) ABSTRACT OF THE DISCLOSURE A process for the production of colored photographic images by the silver dyestuff bleaching process, wherein bleaching is carried out in a dyestuff bleaching bath containing a pyrazine as bleaching catalyst or a pyrazine is added to a bath preceding the dyestuff bleaching bath or wherein photographic material is used that contains at least one layer containing a pyrazine as bleaching catalyst.

The present invention relates to dyestuff bleaching catalysts for the silver dyestuff bleaching process.

As is known, the production of colored photographic images by the silver dyestuff bleaching process is based on the principle that organic dyestuffs, especially azo dyestuffs, are destroyed by metallic silver in suitable baths. Generally, these baths contain a mineral acid, for example, hydrochloric acid, or a strong organic carboxylic acid, potassium bromide and a compound capable of forming silver complexes, for example, thiourea. Theoretically, 4 silver atoms reduce one azo group with formation of colorless amines. However, azo dyestuffs differ greatly from one another in respect of their behaviour in this reduction process, the differences being mainly in the time required to bring about reduction to a colorless substance. Furthermore, the silver dyestuff bleaching process is generally not carried out to its conclusion with utilization of the total amount of metallic silver present, but is tenninated after a certain period after only a proportion of the said silver has been consumed. Thus, during a prolonged bleaching period, bleaching continues at those areas where metallic silver is still present, which means that there may be a paucity of halftones, particularly at areas of low color density.

As is known, a catalyst is required in the bleaching of some azo dyestuffs in order to equal out a large extent the bleaching times for the different dyestuffs and, Where necessary to permit bleaching to a pure white. Compounds that have been proposed as bleaching catalysts, and some of which have been used successfully are, for example, 2:3 dimethylquinoxaline, 2:3 diaminophenazine, 2-hydroxy-3-aminophenazine and anthraquinone sulphonic acid. The catalysts are added to the silver dyestuff bleaching bath in the usual manner, or are incorporated in the photographic color layer. It is also known to add the catalysts to a bath preceding the silver dyestuff bleaching bath. Thus, there are already a number of catalysts and methods of using them available. Nevertheless, the use of catalysts is frequently beset with difficulties. In particular, it is difficult to catalyse the bleaching process in a manner such that the different dyestuffs present in multilayer material are properly attuned to one another as regards bleaching. For example, a particular catalyst can shorten the bleaching time of the yellow and cyan dyestuffs but have no influence on the bleaching time of the magenta dyestuff. Conversely, the magenta dyestuff can respond well to a catalyst and the yellow and cyan dyestuffs remain unaffected. However, it is not only equalling out of the bleaching times that 'is important; it is also vital that 3,394,004 Patented July 23, 1968 gradation be balanced in a manner such that the curves on a graph showing, logarithmically, the dependence of optical density on exposure time are parallel straight lines. The conditions are complicated.

A further disadvantage associated with the bleaching caralysts known hitherto is that the compounds that are effective in low concentrations of about 1 to 10 milligrams per liter as, for example, 2:3 diaminophenazine and 2- hydroxy-3-aminophenazine, have a very pronounced color of their own. This can result in undesirable coloration of the gelatine or support. In contrast to these compounds, the known uncolored catalysts, for example, 2:3-dimethylquinoxaline, have a much weaker action and thus have to to used in larger amounts.

It is therefore desirable to have available as large a number of colorless catalysts as possible in order to be able to bleach the different azo dyestuffs present in the layers in as near as possible the same time and in the same color gradation. In some cases a single catalyst is sufficient, but it may be necessary to use a number of catalysts simultaneously in a suitable concentration. It is also possible to add a catalyst to a bath preceding the silver dyestuff bleaching bath, as mentioned above, and one or more other catalysts are made to act in the silver dyestuff bleaching bath. A combination of bleaching catalysts of the kind defined can be useful when reducing disazo dyestuffs whose reduction proceeds in two distinct steps via an intermediate product that is difficult to reduce. In the case of some disazo dyestuffs, especially cyan disazo or azoxyazo dyestuffs, for example, the well-known symmetrical disazo dyestuff obtained from tetrazotized 3:3- dirnethoxy 4:4 diaminodiphenyl and 1 amino-S-hydroxynaphthalene-Z:4-disulphonic acid, bleaching with the known catalysts, especially at pH values above 2, proceeds in a manner such that only the first azo group is split up and a violet monoazo dyestuff is left in the layers. It is therefore desirable to have catalysts that catalyse the splitting'of the monoazo dyestuff that is produced; the said dyestuff is particularly noticeable and undesirable at the white areas of the image.

The present invention is based on the observation that specially good results are obtained when pyrazines are used as bleaching catalysts in the silver dyestuff bleaching process. The present invention therefore provides a process for the production of colored photographic images by the silver dyestuff bleaching process, wherein bleaching is carried out in a dyestuff bleaching bath containing a pyrazine as bleaching catalyst or a pyrazine is added to a bath preceding the dyestuff bleaching bath or wherein photographic material is used that contains at least one layer containing a pyrazine as bleaching catalyst. The pyrazines possess surprisingly advantageous properties compared with the known dyestuff bleaching catalysts. For example, they are colorless and are effective when used in very low concentrations, and they also catalyse the second reaction step in the case of many known cyan dyestuffs; in other Words, they ensure bleaching of the monoazo dyestuff to colorless cleavage products.

The term pyrazines as used herein refers solely to compounds containing at least one ring of the formula which is not condensed with other rings, which ring may also be depicted in a simplified manner as follows:

The pyrazine ring may carry substituents, for example, this catalyst is capable of promoting the complete bleachcarboxylic acid groups or alkyl groups, for example, ethyl ing of all dyestuffs. When used in higher concentrations groups or especially methyl groups. For example, catalysts it also acts on layers that do not contain silver and is can be used that correspond to the formula thus the cause of so-called bleach-coupling. (3) N 5 The last-mentioned property is much less pronounced in the case of the substitution products of pyrazine, and EFF -Rz the latter have therefore been found to be especially \\N valuable because of their specific action on certain dyestuffs. Compounds possessing this advantage are, for exlh Which 1 and 2 represent hydfoghh atoms, methyl 1O ample, 2:5- and 2:6-dimethylpyrazine. The said dimethylgroups of carboxylic acid groups, and mom especially pyrazines are added to the silver dyestuff bleaching bath lhosfi that correspond to the formula having the composition indicated above in amounts of (4) N\ 0.005 to 0.05 gram per liter. The diethylpyrazines have a Cit-I Zn-l similar action.

J The catalytic action is more greatly reduced in the case Hewlett-1 \N of the pyrazine dicarboxylic acids, it being necessary to h 2 I add, for example, 1 to 2 grams of pyrazine-2:3-dicar- Whlch represents an mleger not gr,eater g i boxylic acid to one liter of dyestuff bleaching bath of the f m there m be mgnlloned f above-mentioned composition in order to achieve the same yllc acid, unsubstituted pyrazine, 2:5-d1methylpyrazine and effect 2:6-d methylpyraz1ne. It IS also poss1ble to use diphenyl- Th silver dyestulf bleaching process is otherwise carpyrazines and acylaminopyrazines, for examp e, comried out in thg usual manner Pounds of the formula The following examples illustrate the invention. Unless (5) R(COO IIN R] otherwise stated, the parts and percentages are by Weight. in which R represents a pyrazine radical, R'(COO---) 20 EXAMPLE 1 represents the radical of an m-basic carboxylic acid, and m represents an integer not greater than 2. Acylaminothis example, the photographlc mateflal d pyrazines of the kind d fi d can be derived f example, tains three colored layers on a support of cellulose acetate from 2-amino-3:6-dimethylpyrazine on the one hand and film, and 1S bill p as fOH'OWSI from a monocarboxylic add f example, benzoic acid, Bottom layer: A red-sensitlzed silver bromide emulslon or a dicarboxylic acid, for example, sebacic acid, terepthcohtalhlhg y dyeshlfi 0f the formula thalic acid or thiophene-Z:S-dicarboxylic acid, on the (a) other.

As has already been indicated, the said pyrazines can COH1 I H (?CH3 Ht) be added to the photographic color layer, to an intermediate layer, to the dyestufi" bleaching bath or to a bath preceding the dyestuff bleaching bath, for example, to the developer, a hardening bath, a stop bath or a special bath H035 "303E l) following the fixing bath. Furthermore, it can also be ad- 40 vantageous to use the pyrazines in conjunction with dye- Hots stuff bleaching catalysts having a different constitution, Second layer: A gelatine intermediate layer. for example, with quinoxalines or phenazines. For ex- Third layer: A green-sensitized silver bromide emulsion ample, the pyrazines can be used as catalysts in combinacontaining a magenta dyestuff of the formula.

(7) NH: HaN

-N=NQ-NHO CNHEHN C 0HN= N=N- OI-I 1103s SOZH HO 1 3 s S|O3H tion with 2:3-diaminodimethylquinoxaline Or with an Fourth layer: A gelatine intermediate layer. aminohydroxyphenazine. 59 Fifth layer: A layer containing a yellow filter dye- Unsubstituted pyrazine is a colorless compound which stuff or colloidal silver acting as yellow filter. greatly accelerates the bleaching of many azo dyestuffs Sixth layer: A silver bromide layer containing a yelwhen added to known silver dyestuff bleaching baths in low dyestutf of the formula HOQS (l)CH3 ERG-(I) SOaH N=NC NHti'lJI-INN=N 0 HsG very small amounts. For example, a powerful bleaching and, if necessary, a covering layer.

effect is achieved with an addition of 0.002 gram of pyra- All layers can be hardened with a halogenated triazine zine per liter of bleaching bath comprising to parts compound, for example, with 2:4-dichloro-6-phenylof hydrochloric acid of 30% strength, 100 to parts amino-1:3:5-triazine-3-sulfonic acid.

of potassium bromide and 80 parts of thiourea dissolved This material is exposed successively in three approin 1,000 parts of water. When used in a highly dilute state, 7 priate spectral regions under a master image and then treated with a developer containing, per liter, 50 grams of anhydrous sodium sulphite, 0.5 gram of 1-phenyl-3- pyrazolidone, 6 grams of hydroquinone, 20 grams of sodium metaborate, 2 grams of potassium bromide and ml. of a 1% aqueous solution of 6-amino-223-dimethylquinoxaline. During development, which takes 12 to minutes, the catalyst penetrates into all layers. The material is washed in water for a short time, and then bleached in a silver dyestuff bleaching bath containing, per liter of water, 30 grams of thiourea, grams of potassium bromide, 70 ml. of hydrochloric acid of 30% strength and 3 ml. of a 1% solution of 2:5-dimethylpyrazine in water. The bleaching time is 8 to 15 minutes. The material is given a short wash with water and then the residual metallic silver is converted into silver halide in the usual manner in a bath containing copper sulphate, hydrochloric acid and potassium bromide. The material is then washed with water, fixed with a 10% solution of ammonium thiosulfate and again washed.

A positive image displaying balanced gradation in all color layers is obtained.

The aminodimethylquinoxaline in the developer can be replaced 'by 2:5-dimethylpyrazine in amounts of 0.005 to 0.01 gram per liter of developer or by 2-amino-3-hydroxyphenazine hydrochloride.

The cyan dyestuff of the Formula 6 in the red-sensitized layer can be replaced by the cyan dyestuff of the formula CHa in which when m =l R represents the radical of a monocarboxylic acid and when mi=2 R represents the radical of a dicarboxylic acid and m represents a whole number of at most 2.

2. In a process for the production of colored photographic images by the silver dyest-utf bleaching method the improvement which comprises carrying out the silver HzC-CHg /CHz-CH H2G\ CH-HN 0H H5Oi-0 O-C2H5 EC NIH-03 OH 15120-0112 CHz-CHz SO3H 11038-- 11035 SOsH EXAMPLE 2 dyestutf bleaching operation in the presence of a pyrazine Photographic material containing colored silver bromide emulsions and gelatine intermediate layers is prepared in the manner described in Example 1. Catalysts are added to the intermediate layers in amounts such that 4 kg. of casting material contains 160 to 230 grams of gelatine (depending on the degree of viscosity required) and also 145 to 500 ml. of an aqueous or alkaline solution of 1.5 grams of the catalyst, for example, pyrazine-2:3-dicarboxylic acid or 2-benzoylamino-3z6-dimethylpyrazine. In a silver dyestuif bleaching bath having the composition indicated in Example 1, the incorporated catalysts diffuse into the dyestutf layer and promote uni form bleaching of the dyestuffs.

EXAMPLE 3 Material having the composition indicated in Example 1 is treated in the manner described in Example 1. However, instead of 3 ml. of a 1% aqueous solution of dimethylpyrazine, 10 to ml. of a 0.2% solution of one of the following pyrazine compounds in methanol are added to the bleaching bath:

of the formula of the formula N f Cn1HZnl in which n represents a whole number of the most 2, as a dyestuff bleaching catalyst.

4. In a process for the production 'of colored photographic images by the silver dyestufif bleaching method the improvement which comprises carrying out the silver dyestuif bleaching operation in the presence of the pyrazine of the formula HaC N .as a dyestuif bleaching catalyst.

5. In a process for the production of colored photographic images by the silver dyestutf bleaching method the improvement which comprises carrying out the silver dyestulr' bleaching operation in the presence of the pyrazine of the formula as a dyestuff bleaching catalyst.

6. In a process for the production of colored photographic images by the silver dyestuff bleaching method the improvement which comprises carrying out the silver dyestutf bleaching operation in the presence of the pyrazine of the formula N Wl-c 0 on COO1I as a dyestuif bleaching catalyst.

7. In a process for the production of colored photographic images by the silver dyestuff bleaching method the improvement which comprises carrying out the silver dyestuff bleaching operation in the presence of the pyrazine of the formula as a dyestutf bleaching catalyst.

8 v 9. In a process for the production of colored photographic images by the silver dyestuflf bleaching method the improvement which comprises canying out the silver dyestuff bleaching operation in the presence of the pyrazine of the formula as a dyestuif bleaching catalyst.

10. In a process for the production of colored photographic images by the silver dyestutf bleaching method the improvement which comprises carrying out the silver dyestuff bleaching operation in the presence of the pyrazine of the formula HaC N as a dyestuff bleaching catalyst.

11. A silver dyestuff bleaching bath containing in Vitus thiourea, potassium bromide, a strong acid and a pyrazine of the formula in which R and R each represents a member selected from the group consisting of a hydrogen atom, a methyl group and a carboxylic acid group as a dyestufi bleaching catalyst.

References Cited UNITED STATES PATENTS 2,270,118 l/1942 Gaspar 96-53 3,156,561 11/1964 Dreyfuss 96-53 I. TRAVIS BROWN, Primary Examiner. 

